electrical potential

1. Electrical Potential
Voltage

2. How can we manipulate energy
in electric fields?
+ +
Apply FORCE to push like charges TOGETHER
FA FA
+ -
FA FA
Apply FORCE to push unlike charges APART

3. Electric Fields
•The electric field can store energy.
Charges gain potential energy when moved against the
field in the same way as masses gain energy when lifted
against gravity.
•The electric field can do work! (remember the
work/energy connection) when they move charges.
Work done against the field to move the charge
equals PE or KE gained by the charge

4. a. In an elevated position, the ram has gravitational potential energy.
When released, this energy is transferred to the pile below.
Electrical Potential Energy

5. a. In an elevated position, the ram has gravitational potential energy.
When released, this energy is transferred to the pile below.
b. Similar energy transfer occurs for electric charges.
Electrical Potential Energy

6. • The energy a charge has due to its
location in an electric field is called
electrical potential energy.
Electrical Potential Energy

7. • If we push a single charge against an electric field,
we do a certain amount of work.
• If we push two charges against the same field, we do
twice as much work.
• Two charges in the same location in an electric field
will have twice the electrical potential energy as one;
ten charges will have ten times the potential energy.
• It is convenient when working with electricity to
consider the electrical potential energy per charge.
Electric Potential

8. The electrical potential energy per charge is the total electrical
potential energy divided by the amount of charge.
At any location, the potential energy per charge—whatever
the amount of charge—will be the same.
The concept of electrical potential energy per charge has
the name, electric potential.
Electric Potential

9. Electrical Potential
• Electrical Potential is also called VOLTAGE or
ELECTRICAL POTENIAL DIFFERENCE, or
POTENTIAL DIFFERENCE
• Unit for electrical potential  VOLT
• 1 Volt = 1 Joule/Coulomb 1V = 1 J/C
q
W
V 
Amount of work done in moving a charge
and
the amount of charge moved

10. 6.0 joules of work are done pushing an object with
3.0 coulombs of charge toward a charged plate.
• How much electrical potential energy was stored in the electric
fields?
• What is the electrical potential difference in the field between
the charged object and the plate?
Example #1
6.0 J
V = W/q
V = 6.0 J / 3.0 C
V = 2.0 V

11. Removing Energy
• This stored energy can also be released.
• What happens to energy that comes OUT
of a field?
– Transfers into kinetic energy
- - - - - - - - - - -
STORING ENERGY
-
-
The field releases
the energy, doing
WORK on the charge!
Example #2
An object with 2 coulombs of charge
is accelerated using an electrical
potential difference of 10 volts.
How much kinetic energy does the
object receive?
V = W
q
W = qV
W = (2C)(10 V)
W = 20 J

12. Example #3
• An object with a charge of -0.5 coulombs is
pushed 0.2 meters toward a negatively charged
plate with a force of 10 newtons.
• What is the energy required to do this?
W = Fd = (10 N)(0.2 m) = 2 J
• What is the potential difference between the
object and the plate after it is pushed?
V = W = 2 J = 4 V
q 0.5 C

13. Example #4
An electron is raised through a potential
difference of 3000 volts.
What is the work done on the electron?
V = W / q
W = Vq = (3000 V)(1.6 x 10-19 C) = 4.8 x 10-16 J

14. Electron-volts
q
W
V  Vq
W 
eV
J
x
C
x
V
W 1
10
6
.
1
)
10
6
.
1
)(
1
( 19
19


 

An electron-volt is the amount of energy
needed to raise 1 elementary charge
through a potential difference of 1 volt.
The electron-volt (eV) is an alternate unit of ENERGY.
Electron-volts are a SHORT CUT to finding
ENERGY when dealing with
ELEMENTARY CHARGES.
What is the energy
needed to raise two electrons to a potential of 1 volt?
W=qV = 2e x 1V
= 2 eV
What is the energy needed to
raise two electrons to a potential of 2.5 volts?
W=qV = 2e x 2.5V
= 5 eV
2 eV = 3.2 x 10-19 J
5 eV = 8.0 x 10-19 J

15. What use is electrical potential?
A battery is a tool that forces
electrons to a higher
electrical P.E. - gives
them VOLTAGE
Higher
VOLTAGE
The electrons naturally “want”
to drop to a lower energy
How do they get there?
We use this by putting a
RESISTOR in the path
of the ELECTRONS – as
they go through
the RESISTANCE they
do WORK on it!
RESISTOR